1. Field of the Invention
The present invention relates to an electronic blood pressure monitor, and more particularly to an electronic blood pressure monitor using a pressurizing section (hereinafter referred to as a xe2x80x9ccuffxe2x80x9d) for pressurizing a portion in one of four limbs and others of a mammal by injecting a fluid such as air thereinto.
2. Description of the Background Art
Among methods measuring a blood pressure using a cuff, there has been available a method in which various kinds of arterial signals (hereinafter referred to as xe2x80x9cpulse wavesxe2x80x9d) originated from changes in inner volume of an artery around which a pressure is applied with the cuff are captured in the course during which a pressure in the cuff (hereinafter referred to as a xe2x80x9ccuff pressurexe2x80x9d) is gradually changed to calculate and determine a blood pressure based on the captured pulse waves. This method is called an oscillometric method.
FIG. 14 is a diagram showing a construction of an electronic blood pressure monitor that is applied to an example in a prior art practice and embodiments of the present invention. The electronic blood pressure monitor of FIG. 14 includes: a microprocessor 1 having, therein, a CPU (an abbreviation of a central processing unit) 1A for intensively controlling and monitoring the electronic blood pressure monitor itself as a center and a memory 1B; a cuff 2, being placed at a predetermined portion of a mammal in order to pressurize an artery; a gradual pressure reduction section 3, a rapid discharging section 4, a pressurizing section 5 and a cuff pressure detecting section 6 all of which are connected to the cuff 2 by an air system; a pulse wave detecting section 7 detecting a pulse wave originating from a change in volume of the artery produced in the course during which the artery is pressurized with the cuff 2; an amplifying circuit-AD (analog-digital) converters 8 and 9; an input interface 10 and an output interface 11. A pressure inside the cuff 2 is controlled by the gradual pressure reduction section 3, the rapid discharging section 4 and the pressurizing section 5.
The CPU 1A of the microprocessor 1 controls other sections. The pressurizing section 5 has a pressure pump, by which the cuff 2 is pressurized to a predetermined cuff pressure. The gradual pressure reduction section 3 has a valve for reducing a cuff pressure. While the valve is closed during pressurization of the cuff 2, it works so as to gradually reduce a cuff pressure when being opened. The rapid discharging section 4 has a valve for reducing a cuff pressure. While the valve is closed during pressurization of the cuff 2, it works so as to rapidly reduce a cuff pressure when being opened. The cuff pressure detecting section 6 has a pressure sensor to detect a cuff pressure. The pulse wave detecting section 7 detects a pulse wave. The amplifying circuit-AD converters 8 and 9 amplify signals outputted from the cuff pressure detecting section 6 and the pulse wave detecting section 7, respectively, to convert the signals to digital values and to give the digital values to the microprocessor 1. The microprocessor 1 processes given data to calculate a blood pressure value and to output a result of the calculation through the output interface 11. The input interface 10 is constituted of switches, buttons and others and installed so as to enable to be externally operable by a user. The output interface 11 is constituted of a display section for displaying information; a printer for printing the information; a speech output section for outputting the information in speech; and others.
A pulse wave is produced by a change in inner volume of an arterial blood vessel, around which an external pressure (a cuff pressure) is applied by pressurization of the cuff 2, due to a balance between the cuff pressure and an pulsating inner pressure (blood pressure). In an oscillometric method, a blood pressure value (at least one of a systolic blood pressure, a diastolic blood pressure and an average blood pressure) is calculated from a pattern of changes in amplitude of pulse waves corresponding to chronological levels of a cuff pressure that changes in the course during which the cuff pressure increases or decreases gradually, for example, stepwise or continuously in a range between a value in the vicinity of a systolic blood pressure (a so-called maximum blood pressure) and a value in the vicinity of a diastolic blood pressure (a so-called minimum blood pressure).
In this method, though a necessity arises for raising a pressure inside the cuff 2 to a value equal to or higher than a systolic blood pressure at the first stage, the systolic blood pressure largely alters according to an individual difference or various factors of the same individual as well, so pressurization has been started after adjusting a pressurization amount given by the pressurizing section 5 in the cuff 5 with an change-over switch provided to the input interface 10. Contradiction arises, however, in adjustment of the pressurization amount performed based on in-advance estimation of a user in an electronic blood pressure monitor with which the user measures a blood pressure since the user uses the electronic blood pressure monitor to measure a blood pressure unknown to the user and such operation has actually been tough to the user.
Therefore, a method has been contrived in which a pulse wave is detected during pressurization of the pressurizing section 5 in the cuff 2 to estimate a systolic blood pressure with a certain precision and to cease pressurization in the cuff 2 at an optimal level based on the estimation. This method is called an automatic pressure setting function and disclosed in JP patents No. 2842696, No. 2936814, No. 2936816, No. 3008582, No. 3042051 and No. 3042052. With the method adopted, a necessity has been removed for a manual operation of a user to adjust a pressurization value through estimation of a systolic blood pressure.
In an oscillometric method, however, since there is still a necessity for gradually reducing a cuff pressure down to a comparative low pressure equal to or lower than a diastolic blood pressure from a high pressure higher than a systolic blood pressure, not only has a user been placed under a restraint in a blood pressure measurement for a long time, which is troublesome to the user, but a problem has also arisen that an environment of usage is restricted and a rapid change in blood pressure cannot be captured though a precision of measurement has become high due to acquirement of information for measuring a blood pressure over a long time, that is to say, due to acquirement of much biogenic information. That is to say, a time is consumed in measurement in the oscillometric method for the reason that a cuff pressure cannot be reduced at a high speed in order to maintain a precision.
In contrast thereto, another method has been proposed in which a measuring time can be shortened even though the measuring method still uses the cuff 2. For simplicity of description of the method, the method is herein called an SPD method (Single Pulse Determination). The SPD method is disclosed in JP patent No. 2745467, No. 2855767 and others. According to an SPD method, a cuff pressure is raised to an arbitrary value to maintain there and a pulse wave signal is captured by one wave or several waves, thereby enabling estimation of a blood pressure value. A construction of an electronic blood pressure monitor to which an SPD method is applied is almost similar to that shown in FIG. 14 only with the exception that no necessity arises for the gradual pressure reduction section 3.
An SPD method uses a change in a waveform of a pulse wave depending on a value of a cuff pressure relative to a blood pressure (hereinafter referred to as a xe2x80x9crelative cuff pressurexe2x80x9d). To briefly describe a principle thereof, a cuff pressure is at first raised to an arbitrary value to then capture at least one pulse wave and to obtain a waveform characteristic amount of the pulse wave. The term, a waveform characteristic amount, is one obtained by quantifying characteristics of a waveform of a wave pulse. Then, a wave form characteristic amount is compared with a predetermined function defining a relationship between a relative cuff pressure and a waveform characteristic amount of a pulse wave to estimate a relative cuff pressure at the time when the pulse wave is captured. Finally, a value of the estimated relative cuff pressure is subtracted from a known cuff pressure (hereinafter referred to as an absolute cuff pressure) detected by the cuff pressure detecting section 6 at the time when the pulse wave was captured; thereby estimating a blood pressure.
According to an SPD method, in such a way, changes in pulse waves (changes in amplitude) are not captured while a cuff pressure is altered over a wide range as done in an oscillometric method but a blood pressure is estimated from the absolute value of a waveform characteristic amount of one pulse wave, thereby, enabling calculation of a blood pressure value from one pulse wave according to the principle. Therefore, since a necessity arises only for a very short time length during which a user is placed under restraint in measurement of a blood pressure, advantages are attained that detection of even a rapid change in blood pressure can be achieved, measurement can be done at anytime and anywhere without selecting an environment of usage and the measurement is comfortable without a pain accompanied therewith. An SPD method, however, is very much reduced in measuring time, but contrary to this, a case has arisen where a precision is insufficient for a particular user since a blood pressure is determined from less of biogenic information and an individual difference is present in a relationship between a relative cuff pressure and a waveform characteristic amount.
In this way, since blood pressure measurements of an oscillometric method and an SPD method have respective characteristics conflicting with each other, a desire has been arisen that a user selectively uses one of the measuring methods according to a situation such as a time, a place or the like. That is to say, there has been a desire of selective use of the methods according to a situation that a user at work measures a blood pressure in a short time period with a blood pressure measurement of a SPD method but the user at home measures a blood pressure in an enough time that is allowed to spend with a good precision using an oscillometric method. However, since there have not been available an electronic blood pressure monitor having both functions of blood pressure measurement of an oscillometric method and an SPD method, a user has had to purchase electronic blood pressure monitors of an oscillometric method and an SPD method, which negates an economy.
Furthermore, though an SPD method is very much reduced in measuring time, a case has been encountered where a precision is not sufficient for a need of a particular user, so a necessity has been arisen for adjusting a relationship between a relative cuff pressure and a waveform characteristic amount with information showing characteristics of a pulse wave different according to an individual to calibrate a result of measurement in an application requiring a high precision. The information used for calibration of a result of measurement is hereinafter referred to as calibration information. In other words, both of electronic blood pressure monitors of a SPD method and a prior art electronic blood pressure monitor are both operated, separately purchasing an electronic blood pressure monitor in the prior art (for example, an electronic blood pressure monitor according to an oscillometric method) for use in calibration to obtain calibration information when a precision is required, and a value of the prior art electronic blood pressure monitor, that is to say, calibration information, has to be inputted to an electronic blood pressure monitor of an SPD method, having lead to requirement of a complicated operation.
Though an SPD method can calculate a blood pressure in a procedure in which the cuff 2 is pressurized to an arbitrary value to capture at least one pulse wave under the pressure from the principle thereof, a pulse wave transmitted from a mammal is very weak in a case where a pressurization value is raised to a value excessively larger than a blood pressure, which increases a noise component in a relatively large value, that is to say, deteriorates an S/N ratio, to disable a waveform characteristic amount of a pulse wave to be correctly calculated, having also resulted in a problem to produce a large error.
Therefore, it is an object of the present invention to provide an electronic blood pressure monitor capable of performing measurement of a blood pressure in a shorter time and with more of correctness.
It is another object of the present invention to provide an electronic blood pressure monitor capable of realizing functions of blood pressure measurement in a shorter time and blood pressure measurement with more of correctness in the same and one construction thereof.
An electronic blood pressure monitor according to an aspect of the present invention includes a cuff configured to be mounted on a predetermined portion of a subject for pressurizing an artery of the subject, a cuff pressure controller for controlling a cuff pressure inside the cuff, a pressure detector for detecting the cuff pressure, a pulse wave detector for detecting a pulse wave of the artery that is pressurized by the cuff, and a first blood pressure measuring portion and a second blood measuring portion being selectively used by the electronic blood pressure monitor at a time.
The first blood pressure measuring portion includes a first blood pressure calculation unit and a calibration unit for calibrating the second blood pressure measuring portion. The first blood pressure calculating unit calculates and outputs a blood pressure of the subject based on a set of cuff pressures chronologically detected by the pressure detector during a period in which the cuff pressure is gradually changed by the cuff pressure controller and on amplitudes of the pulse waves detected by the pulse wave detector at the timings of the corresponding cuff pressure detection by the pressure detector.
The second blood pressure measuring portion includes a parameter measuring unit, a function memory, a function selection unit and a second blood pressure calculating unit.
The parameter measuring unit provides a measured value of pulse wave parameter based on at least one of the pulse waves detected by the pulse wave detector, the pulse wave parameter being indicative of a waveform of the pulse wave that represents a relative cuff pressure corresponding to a pressure difference between the detected cuff pressure and the blood pressure of the subject.
The function memory stores a function of the relative cuff pressure including a set of sub-functions.
A function selection unit selects one of the sub-functions that corresponds to a level of the measured value of the pulse wave parameter.
A second calculating unit identifies the relative cuff pressure based on the selected sub-function and calculates the blood pressure of the subject subtracting the identified relative cuff pressure from the cuff pressure detected by the pressure detector at the time of the pulse wave detection.
The calibration unit includes a data gathering unit that gathers, for each of the pulse waves detected during an operation of the first blood pressure measuring portion at the timings of the corresponding cuff pressure detection, the corresponding relative cuff pressure and the corresponding measured value of the pulse wave parameter, and a data updating unit that modifies the function based on the relative cuff pressures and the corresponding measured values of the pulse wave parameter that are gathered by the data gathering unit.
Therefore, since the first blood pressure measuring portion further includes the calibration unit that calibrates the second blood pressure measuring portion, improvement can be realized on a precision of blood pressure measurement using the second blood pressure measuring portion that can measure a blood pressure in a shorter time while practically enabling exclusion of a complicated calibrating operation.
To practically enable exclusion of the calibrating operation means to complete calibration by the calibration unit during measurement of a blood pressure performed by a user in advance with the first blood pressure measuring portion, to be detailed. In other words, the data gathering unit gathers calibration information necessary for calibration of the second blood pressure measuring portion, that is to say, a blood pressure value calculated by the first blood pressure measuring portion at the time of blood pressure measurement, and pulse wave parameters (a characteristic amount) from one wave or several waves over a wide relative pressure range with the blood pressure value as a reference, and the data updating unit modifies values of functions corresponding to the pulse wave parameters in the function memory using the gathered relative cuff pressures and the corresponding values of the pulse wave parameters with respect to the pulse wave parameters; therefore, the user simply performs blood pressure measurement with the first blood pressure measuring portion without requiring any specific operation in addition.
Furthermore, an electronic blood pressure monitor includes: the first blood pressure measuring portion capable of calculating a blood pressure at a high precision using much of biogenic information though a time is required since a blood pressure is calculated during a period in which the cuff pressure is gradually changed; and a second blood pressure measuring portion completing measurement in a short time though a fluctuation in precision of measurement arises according to an individual difference with less of biogenic information since a blood pressure is calculated using at least one pulse wave.
Therefore, since blood measuring functions with respective different workings and characteristics are integrated in the same electronic blood pressure monitor, no necessity arises for separately purchasing blood pressure monitors with blood pressure measuring functions with respective different workings and characteristics, which is convenient and economical to a user.
Since the same electronic blood pressure monitor integrally has the two kinds of blood pressure measuring functions, different in operation and feature from each other in construction, a manufacturing cost of the equipment can be greatly reduced without a necessity for separate manufacture of two electronic blood pressure monitors.
Furthermore, if both functions are built in, for example, a microprocessor or the like in design and the measuring functions are selectively changed over therebetween by setting on a small scale, products with respective different functions working on different principles can also be manufactured in a single manufacture line.
According to another aspect of the present invention, an electronic blood pressure monitor is of a construction including: a cuff configured to be mounted on a predetermined portion of a subject for pressurizing an artery of the subject; a cuff pressure controller for controlling a cuff pressure inside the cuff; a pressure detector for detecting the cuff pressure; a pulse wave detector for detecting a pulse wave of the artery that is pressurized by the cuff and further includes a first blood pressure measuring portion and a second blood measuring portion being selectively used by the electronic blood pressure monitor at a time.
The first blood pressure measuring portion includes: a first blood pressure calculating unit. The first blood pressure calculating unit calculates and outputs a blood pressure of the subject based on a set of cuff pressures chronologically detected by the pressure detector during a period in which the cuff pressure is gradually changed by the cuff pressure controller and on amplitudes of the pulse waves detected by the pulse wave detector at the timings of the corresponding cuff pressure detection by the pressure detector.
The second blood pressure measuring portion includes: a parameter measuring unit; a function memory; and a function selection unit; and a second blood pressure calculating unit.
The parameter measuring unit provides a measured value of pulse wave parameter based on at least one of the pulse waves detected by the pulse wave detector, the pulse wave parameter being indicative of a waveform of the pulse wave that represents a relative cuff pressure corresponding to a pressure difference between the detected cuff pressure and the blood pressure of the subject.
The function memory stores a function of the relative cuff pressure including a set of sub-functions.
A function selection unit selects one of the sub-functions that corresponds to a level of the measured value of the pulse wave parameter.
A second calculating unit identifies the relative cuff pressure based on the selected sub-function and calculates the blood pressure of the subject subtracting the identified relative cuff pressure from the cuff pressure detected by the pressure detector at the time of the pulse wave detection.
In such a way, an electronic blood pressure monitor includes: the first blood pressure measuring portion capable of calculating a blood pressure at a high precision using much of biogenic information though a time is required since a blood pressure is calculated during a period in which the cuff pressure is gradually changed; and a second blood pressure measuring portion completing measurement in a short time though a fluctuation in precision of measurement arises according to an individual difference with less of biogenic information since a blood pressure is calculated using at least one pulse wave.
Therefore, since blood pressure measuring functions with respective different workings and characteristics are integrated in the same electronic blood pressure monitor, no necessity arises for separately purchasing blood pressure monitors with blood pressure measuring functions with respective different workings and characteristics, which is convenient and economical to a user.
Since the same electronic blood pressure monitor integrally has the two kinds of blood pressure measuring functions, different in operation and feature from each other in construction, a manufacturing cost of the equipment can be greatly reduced without a necessity for separate manufacture of two electronic blood pressure monitors.
Furthermore, if both functions are built in, for example, a microprocessor or the like in design and the measuring functions are selectively changed over therebetween by setting on a small scale, products with respective different functions working on different principles can also be manufactured in a single manufacture line.